Its a standard military light switch.
From left to right you have -
HST - Headlights, side lights and tail lights - This is the one you use most
ST - Side lights and tail lights
T - Just tail lights
OFF - All off (brake lights, horn, hazards etc all work as normal)
CONV - All lights including brake lights and horn etc disabled. This is a tactical setting. There is a convoy light that shines on the rear diff.
SCONV - As above but with front side lights on too
The switch doesnt look complete though. Also you shouldnt have any need for CONV or SCONV settings outside of the army. HST, ST, T and OFF are all safe to use. You still get full functioning brake lights and horns etc in these settings.
Also everyone is talking about british military spec on here. That land rover doesnt have any of the wolf features that you would expect a wolf to have. Is it ex Bangladesh army? The doors, lights, wings, wing tops, bonnet, light surrounds, wheels etc arent wolf spec.